Fluid flow behaviour in vesicular basalt samples from the Skoll High, Vøring Margin.

Area of Science:

• Geology
• Geophysics
• Earth Science

Background:

• Limited research exists on the basalt reservoir and flow properties of the mid-Norwegian margin.
• Subsurface conditions and in-situ fluid flow responses to pore fluid changes are critical for carbon sequestration but understudied.
• Basaltic lava flows are potential reservoirs for carbon sequestration, necessitating an understanding of their hydraulic properties.

Purpose of the Study:

• To investigate the fluid flow properties of basaltic lava flows from the Skoll High, Vøring Margin under simulated subsurface conditions.
• To assess the impact of alteration and pore fluids on the hydraulic properties of these basalts for carbon sequestration applications.
• To compare in-situ brine flow with ambient gas permeability measurements.

Main Methods:

• Collected 32 lava flow samples from IODP Sites U1571/U1572.
• Measured hydraulic properties (porosity, permeability) at ambient conditions.
• Conducted multi-stress, multi-fluid core flooding experiments on a representative sample using X-ray micro-computed tomography (µCT).

Main Results:

• Petrographic analysis revealed significant alteration with secondary clays (smectite) lining pores.
• Helium porosities were generally below the percolation threshold.
• Klinkenberg-corrected nitrogen-gas permeability showed weak correlation with porosity and no depth dependence.
• Brine permeability was four orders of magnitude lower than gas permeability.
• CO2 injection did not notably reduce brine flow; brine-induced clay swelling reduced fluid accessibility.

Conclusions:

• Ambient gas permeability measurements may not accurately reflect in-situ fluid flow in altered basalts.
• Swelling clays and low matrix permeability in altered vesicular basalts can limit injectivity for carbon sequestration.
• Fractures may be essential for significant fluid injectivity in these basaltic formations.